1. Field of the Invention
The present invention relates generally to actuator driving circuits employed, for example, in for recording information signals on or reproducing information signals from an optical disc, and more particularly, is directed to improvements in a circuit for driving an actuator which is operative to actuate, for example, a focus control unit, a tracking control unit or a head shifting unit provided in an apparatus for recording information signals on or reproducing information signals from an optical disc.
2. Description of the Prior Art
There has been proposed an optical disc recording and reproducing apparatus for recording an information signal such as a video or audio signal on an optical disc and reproducing the information signal from the optical disc. One example of the optical disc recording and reproducing apparatus proposed previously is constituted as shown in FIG. 1.
In FIG. 1, an optical disc 1 on which an information recording area is provided is rotated by a spindle driving motor 2 at a predetermined rotational speed. An optical head device 3 is provided to cause a light beam to impinge upon the information recording area of the optical disc 1 and a recording and reproducing circuit 4 is connected to the optical disc 1 for supplying the optical head device 3 with a recording signal and for obtaining a reproduced information signal based on information read from the optical disc 1 by the optical head device 3. Further, a signal processing circuit 5 which is operative to process the reproduced information signal and supply a signal input and output circuit 6 with the reproduced information signal processed therein and to process an input record signal applied thereto through the signal input and output circuit 6 and supply the recording and reproducing circuit 4 with the input record signal processed therein.
A focus servocontrol block 7 is provided for controlling an actuator for focus control contained in the optical head device 3 in response to a focus error signal obtained from the recording and reproducing circuit 4, and a tracking servocontrol block 8 is provided for controlling an actuator for tracing control contained also in the optical head device 3 in response to a tracking error signal obtained from the recording and reproducing circuit 4. A head shifting block 9 is also provided for shifting the position of the optical head device 3 in a direction of the radius of the optical disc 1 in response to a control signal obtained from the tracking servocontrol block 8.
Further, A controller 10 which may be constituted by a microcomputer is provided for controlling each of the recording and reproducing circuit 4, signal processing circuit 5, signal input and output circuit 6, focus servocontrol block 7, tracking servocontrol block 8 and heads shifting block 9.
In such an optical disc recording and reproducing apparatus, it is generally preferable to apply a low power supply voltage to circuits for processing various signals and various control circuits so that each of the circuits is caused to operate by the low power supply voltage with reduced power consumption. However, particularly in the tracking servocontrol block 8, when a tracking actuator driving circuit which is operative to move an objective lens contained in the optical head device 3, through which the light beam impinges upon the optical disc 1, in the direction of the radius of the optical disc 1 for tracking servocontrol is arranged to operate with the low power supply voltage, the operation of the tracking actuator driving circuit is attended with a disadvantage that the moving speed of the optical lens in the optical head device 3 is reduced to be relatively low and therefore a period required for shifting the light beam impinging upon the optical disc 1 by a track jump operation so as to cause the same to form a light beam spot at a desired position on the optical disc 1 is undesirably increased.
In view of this, there has been also proposed a circuit arrangement for driving actuators contained in an optical head device in which different power supply voltages are applied to actuator driving circuits under a condition wherein normal servocontrol operations are carried out and under a condition wherein the track jump operation is carried out, respectively, as disclosed in the Japanese patent application published before examination under the publication number 64-8515. FIG. 2 shows the circuit arrangement thus proposed previously.
Referring to FIG. 2, a focus error signal Ef is supplied through an amplifier 11 to a focus actuator driving circuit 13 which is operative to drive an electromagnetic coil Lf of an actuator contained in an optical head 16 for focus servocontrol in accordance with the focus error signal Ef supplied thereto. Similarly, a tracking error signal Et is supplied through an amplifier 12 to a tracking actuator driving circuit 14 which is operative to drive an electromagnetic coil Lt of an actuator contained in the optical head 16 for tracking servocontrol in accordance with the tracking error signal Et supplied thereto. Further, the tracking error signal Et amplified by the amplifier 12 is supplied to a low pass filter (L.P.F.) 18 which produces a control signal Sh based on the tracking error signal Et and the control signal Sh obtained from the low pass filter 18 is supplied to a head driving circuit 15 which is operative to drive a motor Mh for moving the optical head 16 in a direction of the radius of an optical disc, upon which a light beam from the optical head 16 impinges, in accordance with the control signal Sh supplied thereto.
In addition to the above, a power supply voltage generator 19 is provided for producing a first power supply voltage V1 and a second power supply voltage V2 which is higher than the first power supply voltage V1. One of the first and second power supply voltages V1 and V2 is selected by a switching circuit 17 to be applied to each of the focus actuator driving circuit 13, the tracking actuator driving circuit 14 and the head driving circuit 15. The switching circuit 17 to which a switching control signal Ss is supplied is operative to select the first power supply voltage V1 for applying the same to each of the focus actuator driving circuit 13, the tracking actuator driving circuit 14 and the head driving circuit 15 when the switching control signal Ss represents a first operating condition wherein the tracking actuator driving circuit 14 is working for a normal tracking servocontrol operation and to select the second power supply voltage V2 for applying the same to each of the focus actuator driving circuit 13, the tracking actuator driving circuit 14 and the head driving circuit 15 when the switching control signal Ss represents a second operating condition wherein both of the tracking actuator driving circuit 14 and the head driving circuit 15 are working for the track jump operation.
Therefore, in the circuit arrangement shown in FIG. 2, each of the focus actuator driving circuit 13, the tracking actuator driving circuit 14 and the head driving circuit 15 is supplied with the first power supply voltage V1 which is relatively low so as to operate with reduced power consumption when the normal tracking servocontrol operation is carried out and with the second power supply voltage V2 which is relatively high so that the light beam impinging upon the optical disc is able to be quickly moved into a desired position on the optical disc when the track jump operation is carried out.
However, when an optical disc recording and reproducing apparatus which employs the circuit arrangement for driving actuators contained in an optical head device as described above is subjected to shocks or vibrations caused by external force under a condition wherein the tracking actuator driving circuit 14 is in operation with the first power supply voltage V1 which is relatively low for the normal tracking servocontrol operation, the tracking error of the light beam impinging upon the optical disc could possibly suddenly increase so as to cause a relatively large noise contained in the tracking error signal Et which is supplied to the tracking actuator driving circuit 14. Consequently, the tracking actuator driving circuit 14 operating with the first power supply voltage V1 which is relatively low and therefore having an output dynamic range not so wide produces an output having a level limited to be constant in response to a large level portion of the noise contained in the tracking error signal Et, so that the tracking servocontrol can no longer be operated correctly and an undesirable track shift movement of the light beam impinging upon the optical disc, in which the light beam shifts or jumps to another record track adjacent to the former record track on the optical disc, is caused.